More than 30 autoimmune diseases are presently known; these include many which have received much public attention, including myasthenia gravis (MG) and multiple sclerosis (MS). Characteristic of these diseases is the attack by the immune system on the tissues of the victim--these tissue antigens being resistant in non-diseased individuals because of their recognition by the immune system as "self". In autoimmune diseases, this recognition apparently does not occur, and the tissue of the afflicted subject is treated as an invader--i.e., the immune system sets about destroying this presumed foreign target.
A crude approach to treating autoimmune disease is, of course, general immunosuppression. This has the obvious disadvantage of crippling the ability of the subject to respond to real foreign materials to which it needs to mount an immune response. An only slightly more sophisticated approach relies on the removal of antibodies or immune complexes involving the target tissue. This also has adverse side effects, and is difficult to accomplish. The invention approach, described in detail below, relies on a "clonotypic" reagent--i.e., a reagent which attacks only the cells of the immune system which are responsive to the autoantigen.
In the general paradigm now considered to describe the immune response, specific antigens presented result in a clonal expansion, as first proposed by Burnet in 1959. According to this scenario, a particular subject will have hundreds of thousands of T and B cells each bearing receptors that bind to different antigenic determinants. Upon exposure to an antigen, the antigen selectively binds to cells bearing the appropriate receptors for the antigenic determinants it contains, ignoring the others. The binding results in a cloned population of thousands of daughter cells, each of which is marked by the same receptor. A clonotypic reagent affects only a subset of the T and B cells which are appropriate for the antigen of interest. In the case of the invention compositions, the antigenic determinant is usually that associated with an autoimmune disease.
The clonotypic reagent compositions of the invention are specifically designed to target T-helper cells which represent the clones specific for the antigenic determinant(s) of the tissue which is affected by the autoimmune disease. T-helper cells recognize a determinant only in association with an MHC protein; the complexes of the invention therefore include an effective portion of the MHC protein.
There have, recently, been some related approaches which attempt to interdict the immune response to specific antigens. For example, the autoantigen thyroglobulin has been conjugated to ricin A and the conjugate was shown to suppress specifically the in vitro antibody response of lymphocytes which normally respond to this antigen. It was suggested that such immunotoxins would specifically delete autoantibody-secreting lymphocyte clones (Rennie, D. P., et al, Lancet (Dec. 10, 1983) 1338-1339). Diener, E., et al, Science (1986) 231:148-150 suggested the construction of compounds which cause antigen-specific suppression of lymphocyte function by conjugating daunomycin to the hapten (in this case, of ovalbumin) using an acid-sensitive spacer. The conjugate caused hapten-specific inhibition of antibody secretion by B lymphocytes in vitro and in vivo. A conjugate of daunomycin (with an acid-sensitive spacer) to a monoclonal antibody-specific to T-cells also eliminated the response by T-lymphocytes to concanavalin A. Steerz, R. K. M., et al, J Immunol (1985) 134:841-846 utilized radiation as the toxic element in a toxin conjugate. Rats were administered a radioactively labeled, purified receptor from electric fish, prior to injection with cold receptor. Injection with this receptor is a standard procedure to induce experimental autoimmune myasthenia gravis (EAMG). Control rats that received preinjection only either of cold receptor or radiolabeled albumin, prior to administration of receptor to induce the disease develop the symptoms of EAMG; those pretreated with radioactively-labeled receptor showed reduced symptoms. It was surmised that the labeled, and therefore destructive, receptor selectively eliminated immunocompetent cells. Similar work utilizing a ricin/receptor conjugate for pretreatment was reported by Killen, J. A., et al, J Immunol (1984) 133:2549-2553.
A less specific approach which results in the destruction of T-cells in general is treatment with an IL-2/toxin conjugate .as reported by Hixson, J. R., Medical Tribune (Jan. 28, 1985) 4-5. In a converse, but related, approach Liu, M. A., et al, Science (1988) 239:395-397, report a method to "link up" cytotoxic T-cells with a desired target, regardless of the cytotoxic T-cell specificity. In this approach, antibody specific to the universal cytotoxic T-lymphocyte receptor CD3 was conjugated to a hormone specific for a surface receptor on the target tumor cell. The conjugate was capable of activating cytotoxic T-lymphocytes to destroy human melanoma cells when melanocyte-stimulating hormone was the hormone used.
The invention compositions and methods are designed to target helper T-cells which recognize a particular antigen in association with a glycoprotein encoded by the major histocompatibility complex (MHC). The current model of immunity postulates that antigens mobilize an immune response, at least in part, by being ingested by an antigen-presenting cell (APC) which contains on its surface a Class II glycoprotein encoded by a gene in the MHC. The antigen is then presented to a specific T helper cell in the context of the surface-bound MHC glycoprotein, and by interaction of the antigen-specific T-cell receptor with this antigen-glycoprotein complex, the T helper cell is stimulated to mediate the antigen-specific immune response, including induction of cytotoxic T-cell function, induction of B cell function, and secretion of a number of factors aiding and abetting this response.
The involvement of the MHC Class II proteins in autoimmune disease has been shown in animal models. Administration of antibodies to either MHC Class II proteins themselves or antibodies to agents that induce expression of the MHC Class II genes interferes with development of the autoimmune condition in these model systems. The role of helper T-cells has also been demonstrated in these models by counteracting the autoimmune system using anti-CD4 monoclonal antibodies; CD4 is the characteristic helper T-cell receptor (Shizuru, J. A. et al, Science (1988) 240:659-662).
The invention complexes effectively substitute for the antigen-presenting cell in evoking the interaction of the T-lymphocytes and other cells of the immune system with respect to the antigen. It has been shown that isolated MHC Class II antigen in and of itself can effectively replace the antigen-presenting cell in the presentation of antigen epitopes to a T-helper lymphocyte (Watts, T. H., et al, Proc Natl Acad Sci USA (1984) 81:7564-7568. However, by substituting an effector function, such as a toxin, for the antigen presenting cell (APC) surface, the antigen is made effective in destroying the immune response it would otherwise create; by substituting a label for the APC surface, the antigen is caused to identify the portions of the immune system with which it interacts.